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United States Patent |
5,774,305
|
Boutaghou
|
June 30, 1998
|
Head gimbal assembly to reduce slider distortion due to thermal stress
Abstract
The present invention is directed to a head gimbal assembly which
effectively reduces the membrane forces and membrane moments generated
between the slider and the gimbal by adding geometric patterns distributed
on the gimbal support. The head gimbal assembly of the present invention
comprises the support coupled to the slider at an interface wherein the
support includes a plurality of spaced apart markings or etchings at the
interface. The head gimbal assembly of the present invention provides for
localized deformations of the slider which avoid the bulk deformations
that cause undesirable transducer displacement.
Inventors:
|
Boutaghou; Zine-Eddine (Rochester, MN)
|
Assignee:
|
Seagate Technology, Inc. (Scotts Valley, CA)
|
Appl. No.:
|
486009 |
Filed:
|
June 7, 1995 |
Current U.S. Class: |
360/245.4 |
Intern'l Class: |
G11B 005/48; G11B 021/16 |
Field of Search: |
360/103,104
|
References Cited
U.S. Patent Documents
4700250 | Oct., 1987 | Kuriyama | 360/104.
|
5333085 | Jul., 1994 | Prentice et al. | 360/104.
|
5452158 | Sep., 1995 | Harrison et al. | 360/104.
|
5499153 | Mar., 1996 | Uemura et al. | 360/103.
|
5612840 | Mar., 1997 | Hiraoka et al. | 360/104.
|
Foreign Patent Documents |
2-31390 | Feb., 1990 | JP | 360/104.
|
Primary Examiner: Levy; Stuart S.
Assistant Examiner: Korzuch; William R.
Attorney, Agent or Firm: Westman, Champlin & Kelly, P.A.
Claims
What is claimed is:
1. A head gimbal assembly for a magnetic disc drive, comprising:
a slider;
a gimbal having an interface, defining a plane, attached to the slider; and
discontinuity means for localizing deformation of the slider and gimbal
when the head gimbal assembly is subjected to thermal stress, the
discontinuity means positioned whereby any linear cross section through
the gimbal interface perpendicular to the plane of the interface
intersects the discontinuity means.
2. A head gimbal assembly for a magnetic disc drive, comprising:
a slider formed of a material having a first coefficient of thermal
expansion;
a gimbal formed of a material having a second coefficient of thermal
expansion different from the first coefficient of thermal expansion, the
gimbal having an interface attached to the slider, wherein the interface
has a bonding area defining a plane and fixing the gimbal to the slider
which includes a plurality of discontinuities positioned whereby any
linear cross section through the bonding area and perpendicular to the
plane includes at least one discontinuity; and
wherein the discontinuities are spaced and sized to reduce thermal stresses
between the slider and the gimbal.
3. The head gimbal assembly of claim 1 wherein the gimbal includes a
support, wherein the interface is at the support.
4. The head gimbal assembly of claim 3 wherein the plurality of
discontinuities includes a plurality of recesses in the support.
5. The head gimbal assembly of claim 4 wherein the plurality of recesses
are randomly distributed on the support.
6. The head gimbal assembly of claim 3 wherein the plurality of
discontinuities includes a plurality of holes through the support.
7. The head gimbal assembly of claim 6 wherein the plurality of holes are
randomly distributed about the support.
8. The head gimbal assembly of claim 3 wherein the slider is attached to
the support via an adhesive.
9. A gimbal for use with a slider formed of a material having a first
coefficient of thermal expansion, the gimbal comprising:
a support formed of a material having a second coefficient of thermal
expansion different from the first coefficient of thermal expansion, the
support hating an interface which has a bonding area defining a plane, the
interface adapted to be coupled to the slider, wherein the support
includes a plurality of spaced-apart discontinuities positioned whereby
any linear cross section through the plane perpendicular to the plane of
the bonding area includes at least one discontinuity, and wherein the
discontinuities are sized and spaced to reduce thermal stresses between
the slider and the support.
10. The gimbal of claim 9 wherein the discontinuities are randomly
distributed on the support.
11. The gimbal of claim 10 wherein the discontinuities include holes
through the support.
12. The gimbal of claim 9 wherein the discontinuities include recesses in
the support.
13. A magnetic disc drive system, comprising:
a magnetic storage disc;
an actuator arm having a head gimbal assembly attached thereto, the head
gimbal assembly formed of a material having a first coefficient of thermal
expansion wherein the head gimbal assembly includes a transducer formed of
a material having a second coefficient of thermal expansion, the
transducer attached to the head gimbal assembly and disposed adjacent to
the disc; and
wherein the head gimbal assembly includes a support having a bonding area
defining a plane and coupling the head gimbal assembly to the transducer,
the support including a plurality of discontinuities for permitting
localized deformation when the transducer and support are subjected to
thermal stress, which discontinuities are positioned whereby any linear
cross section through the bonding area and perpendicular to the plane
includes at least one discontinuity.
14. The magnetic disc drive system of claim 13 wherein the discontinuities
are formed by a plurality of geometric patterns which extend through the
support.
15. The magnetic disc drive system of claim 13 wherein the discontinuities
are formed by a plurality of geometric patterns which are recessed in the
support.
16. The magnetic disc drive system of claim 13 wherein the discontinuities
are randomly distributed on the support.
Description
BACKGROUND OF THE INVENTION
The present invention relates to a gimbal for supporting a hydrodynamic air
bearing slider over a rotating magnetic medium. More specifically, the
present invention relates to a gimbal which reduces slider distortion due
to thermal stress.
Disc drives are the primary devices employed for mass storage of computer
programs and data. The advantages of disc drive technology over other
means of data storage include a lower cost per unit of storage capacity
and a generally higher transfer rate. Within a disc drive, a load beam
supports a hydrodynamic air bearing slider close to a rotating magnetic
disc. The load beam supplies a downward force that counteracts the
hydrodynamic lifting force developed by the slider's air bearing. The
slider carries a magnetic transducer for communication with individual bit
positions on the rotating magnetic disc.
A gimbal is positioned between the load beam and the slider. The gimbal
resiliently supports the slider and allows it to pitch and roll while it
follows the topography of the rotating disc. As such, the gimbal is a
crucial element in a magnetic disc drive unit.
Typically, the gimbal is welded to the load beam and is connected to the
slider by an adhesive to form a head gimbal assembly. For example, with
various types of gimbals such as "ring-type" and "beam-type" gimbals, the
slider is adhesively bonded to a central tongue, or "support" as it is
generally called, which is supported by resilient beams. This adhesive
bond presents several concerns to a gimbal designer.
Among these concerns is slider distortion due to thermal stresses. The
principle of thermal expansion states that essentially all solids expand
in volume when the temperature is raised. When the temperature is
increased, the average distance between atoms increases, which leads to an
expansion of the whole solid body. The amount of thermal expansion is
dependent upon a property called the coefficient of thermal expansion
which has different values for different materials. In other words,
different materials expand at different rates for a given temperature
change.
In a typical head gimbal assembly, the gimbal is made from stainless steel
which has a substantially different coefficient of thermal expansion than
the slider, which is typically made from alumina. Because the coefficients
of thermal expansion are different and the slider is bonded to the gimbal,
temperature changes cause a net elastic displacement at the support/slider
interface which is responsible for bending and twisting of the slider.
Bending and twisting of the slider causes a net displacement of the
magnetic transducer, and such net displacement adversely affects
transducer performance. Unintended transducer displacement causes the
transducer to read from the wrong track or to be improperly positioned
over the disc. This prevents the transducer from effectively reading data
from and writing data to the magnetic disc which adversely effects the
performance of the computer system.
The effects of thermal distortion at the head gimbal assembly is well known
in the disc drive industry. There are two methods for addressing this
problem, and both methods fall with disfavor. In prior art disc drives,
the effect of thermal distortion is reduced by minimizing the contact area
between the gimbal and the slider or by choosing a soft adhesive to reduce
the net elastic displacement experienced by the support interface. These
methods, however, are tedious to implement and rely on mature
manufacturing processees. Therefore, there is a continuing need for head
gimbal assembly which reduces the effects of thermal distortion yet can be
relatively easily manufactured.
SUMMARY OF THE INVENTION
The present invention is directed to a head gimbal assembly which
effectively reduces the membrane forces and membrane moments generated
between the slider and the gimbal by adding geometric patterns distributed
on the gimbal support. The head gimbal assembly of the present invention
comprises the support coupled to the slider at an interface wherein the
support includes a plurality of spaced apart markings or etchings at the
interface. The head gimbal assembly of the present invention provides for
localized deformations of the slider which avoid the bulk deformations
that cause undesirable transducer displacement.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a plan view of a load arm supporting a head gimbal assembly
embodying features of the present invention over a magnetic disc.
FIG. 2 is a perspective view of the load arm and head gimbal assembly of
FIG. 1.
FIG. 3 is a more detailed side view of the load arm and head gimbal
assembly of FIG. 1.
FIG. 4 is an enlarged plan view of the gimbal shown in FIG. 1.
FIG. 4A is an enlarged plan view of another gimbal embodying features of
the present invention.
FIG. 5 is a schematic partial plan view of a portion of a gimbal embodying
features of the present invention.
FIG. 5A is a schematic partial plan view of a portion of another gimbal
embodying features of the present invention.
FIG. 5B is a schematic partial plan view of a portion of another gimbal
embodying features of the present invention.
FIG. 6 is a schematic partial side view of a portion of a gimbal embodying
features of the present invention, sectioned for clarity.
FIG. 7 is a schematic partial side view of another gimbal embodying
features of the present invention, sectioned for clarity.
FIG. 7A is a schematic partial plan view of a portion of another gimbal
embodying features of the present invention.
FIG. 8 is a schematic side view of a prior art head gimbal assembly
depicting bulk deformation due to thermal stress.
FIG. 9 is a schematic side view of a head gimbal assembly embodying
features of the present invention and depicting localized deformations as
a result of there al stress.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 illustrates an actuator 10 and an actuator arm 12 which supports a
head gimbal assembly 13 over a magnetic disc 16. The actuator 10 positions
the arm 12 along an arc 14 over the magnetic disc 16. The arm 12 includes
a supporting arm 18, a base plate 20, and a load arm 22. The head gimbal
assembly 13 includes a gimbal 24 and a slider 26. The arm 12 is known as
the rotary actuating arm because the actuator 10 rotates the arm 12 to
position the slider 26 along the arc 14.
FIG. 2 is a perspective view of the load arm 22 supporting the head gimbal
assembly 13, as viewed from beneath the load arm 22 in FIG. 1. The gimbal
24 resiliently supports the slider 26 over the disc 16. As the disc 16
rotates, the slider 26 flies over the surface of the disc 16. The gimbal
24 allows the slider 26 to pitch and roll while the slider 26 follows the
topography of the disc 16.
FIG. 3 is a side elevation view of the load arm 22 and the head gimbal
assembly 13. The head gimbal assembly 13 includes the slider 26 and the
gimbal 24. The elongated member 30 of the gimbal 24 is secured to the load
arm 22 in a known manner. In one preferred embodiment of the present
invention, the slider 26 is secured to a tongue 36 by an adhesive
connection at interface 37. When the head gimbal assembly 13 is secured to
the load arm 22, pivot 40 forces the tongue 36 and the slider 26 downward
and into a "loaded" position. In the loaded position, the pivot 40
provides a surface about which the slider 26 can pitch and roll while it
follows the topography of the disc 16.
FIG. 4 is an enlarged plan view of the gimbal 24 embodying features of the
present invention. The gimbal 24 includes a resilient, elongated member 30
having a rearward position 32 and a forward position 34. A cantilevered
tongue 36 is cut from a central region of the forward position 34. The
tongue 36 includes a central pad 38. A pivot 40 is formed from the central
pad 38 for point contact with the load arm 22 (as shown in FIG. 3).
Apertures 42 and 44 are provided for aligning the gimbal 24 with the load
arm 22. The gimbal 24 is shown with a plurality of spaced-apart geometric
patterns 50 preferably randomly distributed on the central pad 38 to which
the slider 26 is adhered at interface 37. Such geometric patterns 50 can
be holes, as shown, recesses or depressions, markings or features that
which otherwise create "discontinuities" in the central pad 38.
FIG. 4A is an enlarged plan view of another gimbal 24a, which is typically
called a 90.degree. gimbal, embodying features of the present invention.
The 90.degree. gimbal has a rearward portion 32a and a forward portion
34a. A cantilevered tongue 36a is cut from a section of the 90.degree.
gimbal 24a proximate the forward portion 34a. The tongue 36a includes a
central pad 38a and a pivot 40a for point contact with a load arm (not
shown). Apertures 42a and 44a are provided for aligning the 90.degree.
gimbal 24a with a load arm (not shown). The central pad 38a also includes
a plurality of geometric patterns 50, creating "discontinuities" as
described above, which are preferably randomly distributed thereon.
As suggested by FIGS. 4 and 4A, a gimbal may assume a wide variety of
configurations. As such, a gimbal may or may not include a central pad 38
or 38afor affixation of the slider 26 thereto. Those skilled in the art
can contemplate a number of means for attaching the slider 26 to a gimbal.
Thus, the portion of the gimbal attached to the slider 26 is generically
referred to in the art as a "suspension" or "support". It is to be
understood that the present invention can be practiced with a support, and
not limited to use only on gimbals 24 and 24a having a tongue 36 or 36a
with a central pad 38 or 38a.
FIG. 5 is schematic plan partial view of the central pad 38, or the like,
which will generically be referred to as a "support", generally referred
to as reference numeral 54, and which is used to interface the gimbal 24
with the slider. In this example, the geometric patterns 50 are uniform
size cross-like holes which are distributed preferably randomly on the
central pad 38. The cross-like holes are preferred because their geometry
permits the holes to be positioned closer together than circular-like
holes. In other words, the overall area which is the central pad 38 is
less than if the geometric patterns 50 were circles, as shown in the
embodiments of FIG. 4 and 4A.
FIGS. 5A and 5B show two other contemplated embodiments of the present
invention in partial plan views of the support 54. In FIG. 5A, the
geometric patterns 50 are of varying size. The size can be randomly
selected, of course. In FIG. 5B, the geometric patterns 50 are of varying
shape. Of course, embodiments are contemplated wherein the size, shape and
distribution of the geometric patterns 50 can be selected.
FIGS. 6, 7 and 7A show schematic side view cross-sections of a support 54,
or the like, used to attach the gimbal 24 with the slider 26 at interface
56. The geometric patterns 50 can be etched into the support during
fabrication of the gimbal 24. The geometric patterns 50 can be either
fully etched so as to create holes 51 through the support 54 as shown in
FIG. 6, or partially etched so as to create depressions 52 as shown in
FIG. 7, or a combination of partially etched depressions 52 or holes 51 as
shown in FIG. 7A. Partial etching of depressions 52 is preferred in order
to handle excess adhesive used in securing the slider 26 to the gimbal 24.
Preferably, the geometric patterns 50 are 100 to 150 microns in diameter.
This size is chosen because it is suited for use with standard etching
techniques. As standard etching techniques become better suited to create
holes or depressions of smaller diameter on the support 54, it is expected
that hole size will decrease in diameter and a greater number of geometric
patterns can be placed on the support 54.
FIG. 8 shows a side schematic view of a support 60 and slider 26 of the
prior art under thermal stress. Because the thermal expansion coefficients
of the slider and the gimbal are substantially different, the elastic
displacements at an interface 62 cause a net elastic displacement
responsible for bending and twisting the slider. Such exaggerated bulk
deformation results in an unduly large net displacement to a transducer 70
attached thereto.
FIG. 9 shows a schematic side view of a head gimbal assembly 13 of the
present invention wherein the gimbal 24 is attached to the slider 26 at
support 54 and under thermal stress. The addition of patterns 50 to the
support 54 create a large number of discontinuities and pivot points where
the stresses are distributed randomly throughout the interface 56, or
contact area, with no preferred orientation. It is desirable to create a
large number of discontinuities, as effected by the geometric patterns 50,
randomly distributed on the support 54 so as not to create any preferred
direction for the membrane moments and forces to be generated. Localized
deformations, as indicated generally at 72, of the slider 26 due to the
geometric patterns 50, avoid the bulk deformation of the prior art.
The present invention is expected to reduce membrane forces and moments
acting on the slider due to thermal stress. The result is a reduced net
displacement of the transducer 70 thus reducing adverse effects on
transducer performance.
Also, because the geometric patterns 50, can be etched directly during the
fabrication of the gimbal spring 24, no additional cost to the parts is
expected, such as using a more expensive soft adhesive as in the prior
art. The geometric patterns 50 or 52 can be laser ablated, punched,
etched, pinched or otherwise perforated. Portions of support 54 can be
masked with a desired pattern. The unmasked portions of the support 54 are
etched to leave the desired pattern in the support 54. The displacement
and rotation of the support 54 is proportional to the modulus of
elasticity of the material and to the thickness cubed and linearly
proportional to the width and length of the support.
Although the present invention has been described with reference to
preferred embodiments, workers skilled in the art will recognize that
changes may be made in form and detail without departing from the spirit
and scope of the invention.
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